"We are currently treating the fire as suspicious and are appealing for anyone who was in the area at around 8.30am to 8.40am, and saw anyone acting suspiciously.

Anyone riding or driving through the Croxley View or Tolpits Lane areas of Watford or Rickmansworth between 8.15am and 9am on Sunday morning, with a helmet camera or dashboard camera that may have recorded an older shape blue Vauxhall Astra that was seen leaving the vicinity of the fire is asked to contact Watford Local Crime Unit on 01923 472978.

Police are keen to trace the users of that vehicle and any potential footage held by members of the public could prove vital to the investigation."

Alternatively, you can contact the independent crime-fighting charity Crimestoppers anonymously on 0800 555 111 or through their Anonymous Online Form at www.crimestoppers-uk.org